The present invention relates to self-ballasted electrodeless discharge lamps and electrodeless discharge lamp operating devices.
With conventional electrodeless discharge lamps, high frequency alternating current is supplied through a coil to generate an alternating magnetic field from the coil and form a plasma within the discharge vessel. Then, ultraviolet light radiated from the plasma is converted into visible light by a phosphor layer that has been applied to the inside surface of the discharge vessel, and light emanates to the outside. An electrodeless discharge lamp of this configuration is disclosed in JP S58-57254A, for example.
However, a problem with this conventional configuration was that the efficiency is much lower than that of discharge lamps with electrodes already in general circulation.
Accordingly, in recent years, electrodeless discharge lamps in which a reflective coating is formed on a portion of the discharge vessel so as to increase the usage efficiency of the generated light have been developed. Such an electrodeless discharge lamp is disclosed in JP H10-199483A, for example. The configuration of a conventional electrodeless discharge lamp having a reflective coating is described below.
FIG. 3 shows the configuration of a conventional electrodeless discharge lamp having a reflective coating. In FIG. 3, mercury and a rare gas are filled into a discharge vessel 21 made of glass, for example. A reflective coating 26 is provided on a portion of the interior side of the discharge vessel 21, and is covered by a phosphor layer 22. The reflective coating 26 is made of aluminum oxide, for example, which reflects light in both the ultraviolet and visible spectrums. A coil 23a is disposed in a cavity portion of the discharge vessel 21. A ballast circuit for supplying high frequency alternating current to the coil 23a is provided within a case 25. The discharge vessel 21 is supported by the case 25, and is configured so that an alternating magnetic field is generated from the coil 23a due to the high frequency alternating current from the ballast circuit. It should be noted that a lamp base 27 is attached to a portion (bottom portion) of the case 25, and is linked to a commercial power source and connected to the ballast circuit.
The operation of the electrodeless discharge lamp shown in FIG. 3 is described next.
First, an alternating magnetic field is generated within the discharge vessel 21 from the coil 23a due to the high frequency alternating current that is supplied from the ballast circuit through the coil 23a. An alternating electric field that cancels out this alternating magnetic field is generated in the discharge vessel 21. That is, an electromagnetic field is generated within the discharge vessel 21. Due to the generated alternating electric field, the mercury and the rare gas in the discharge vessel 21 become excited due to repeated collision motion and form a plasma within the discharge vessel 21, and ultraviolet light is radiated from the plasma. The portion of the radiated ultraviolet light that arrives at the phosphor layer 22 applied other than at the cavity portion of the discharge vessel 21 is converted into visible light by the phosphor layer 22 and emanates directly to the outside. Light that is converted into visible light by the phosphor layer 22 applied to the cavity portion of the discharge vessel 21 arrives at the reflective coating 26, is reflected by the reflective coating 26 and passes through the phosphor layer 22 of the cavity portion, travels through the discharge plasma, and then passes through the phosphor layer 22 other than at the cavity portion of the discharge vessel 21 and emanates to the outside. That is, with this configuration, the visible light generated by the phosphor layer 22 of the cavity portion emanates to the outside, and thus usage efficiency of the light is improved.
The reflective coating 26 that is used in conventional electrodeless discharge lamps is formed by applying a solution of titanium oxide or aluminum oxide powder onto the discharge space side of the cavity portion of the discharge vessel 21. Then, after the reflective coating 26 is applied, the phosphor layer 22 is applied thereon. Thus, any irregularities in the application of the reflective coating 26 result in even larger irregularities, that is, variations in the coating thickness, in the applied phosphor layer 22. The phosphor layer 22 is formed by rare earth phosphor and halophosphate phosphor, and in combinations of these phosphors, there is a need for an ideal layer thickness with respect to the light extraction efficiency. The light extraction efficiency drops if the thickness of the phosphor layer is too thin or too thick. Thus, during the manufacturing process, the viscosity and the relative weight, for example, of the applied solution are adjusted so as to achieve the optimal layer thickness required for the phosphor combination. However, if the surface of the reflective coating 26 on which it is applied is uneven, then the phosphor layer cannot be provided at a uniform thickness through such means of adjustment, and this is a problem because the light extraction efficiency is reduced. Also, because the total coating thickness of the two-layered portion (layer of the reflective coating 26 and the phosphor layer 22) is thick, the strength of the coating is reduced, and this is a problem because the coating may come loose due to minor impacts.
In light of the problems mentioned above, it is an object of the present invention to provide a self-ballasted electrodeless discharge lamp and an electrodeless discharge lamp operation device that efficiently and effectively reflects and utilizes at least one of visible light and infrared light radiated to the cavity portion without the provision of the reflective coating 26 on the discharge space side of the cavity portion in the discharge vessel 21.
A first self-ballasted electrodeless discharge lamp according to the invention is provided with a discharge vessel filled with discharge gas, the discharge vessel having a cavity portion, a coil inserted into the cavity portion of the discharge vessel, a ballast circuit for supplying high frequency power to the coil, and a lamp base that is electrically connected to the ballast circuit, wherein the discharge vessel, the coil, the ballast circuit, and the lamp base are configured as a single unit, and a reflective tape for reflecting light that is radiated from the discharge gas and emitted from the inside of the discharge vessel to its cavity portion side is wound around the coil.
It is preferable that the reflective tape reflects at least one of infrared light and visible light.
It is further preferable that the reflective tape reflects visible light.
It is also preferable that a tube-shaped bobbin around which the coil is wound is further provided.
It is preferable that a reflective plate for reflecting light that is radiated from the discharge gas is further provided between the discharge vessel and the ballast circuit.
In a preferable embodiment, the reflective plate reflects infrared light or visible light.
In another preferable embodiment, the reflective plate reflects visible light.
It is preferable that the coil is wound around a core made of ferrite.
It is further preferable that the reflective tape is also wound around portions of the core surface where the coil is absent.
It is preferable that a phosphor layer is formed on at least a portion of the surface of the inside of the discharge vessel.
A second self-ballasted electrodeless discharge lamp according to the invention is provided with a discharge vessel filled with discharge gas, the discharge vessel having a cavity portion, a coil inserted into the cavity portion of the discharge vessel, a ballast circuit for supplying high frequency power to the coil, and a lamp base that is electrically connected to the ballast circuit, wherein the discharge vessel, the coil, the ballast circuit, and the lamp base are configured as a single unit, and a reflective coating for reflecting light that is radiated from the discharge gas and emitted from the inside of the discharge vessel to its cavity portion side is formed on a surface of a metal wire forming the coil.
A third self-ballasted electrodeless discharge lamp according to the invention is provided with a discharge vessel filled with discharge gas, the discharge vessel having a cavity portion, a coil inserted into the cavity portion of the discharge vessel, a ballast circuit for supplying high frequency power to the coil, and a lamp base that is electrically connected to the ballast circuit, wherein the discharge vessel, the coil, the ballast circuit, and the lamp base are configured as a single unit, and a reflective layer for reflecting light that is radiated from the discharge gas and emitted from the inside of the discharge vessel to its cavity portion side is formed on a surface of the cavity portion that is in opposition to the coil.
An electrodeless discharge lamp operating device according to the invention is provided with a discharge vessel filled with discharge gas, the discharge vessel having a cavity portion, a coil inserted into the cavity portion for generating an electromagnetic field, a ballast circuit for supplying high frequency power to the coil, and a reflection means provided between the discharge vessel and the coil for reflecting light that is radiated from the discharge gas that has discharged due to the electromagnetic field.
It is preferable that the reflection means is selected from a group consisting of a reflective tape, a reflective coating formed on a surface of a metal wire that forms the coil, a reflective layer that is formed on a surface of the cavity portion that is in opposition to the coil, a reflective plate provided between the discharge vessel and the ballast circuit, and a reflective layer formed on the surface of the coil.
It is also possible that a self-ballasted electrodeless discharge lamp of the invention is provided with a discharge vessel filled with discharge gas, the discharge vessel having a cavity portion, a coil inserted into the cavity portion of the discharge vessel, a ballast circuit for supplying high frequency power to the coil, and a lamp base that is electrically connected to the ballast circuit, wherein the discharge vessel, the coil, the ballast circuit, and the lamp base are configured as a single unit, and a reflective layer for reflecting light that is radiated from the discharge gas and emitted from inside the discharge vessel to its cavity portion side is formed on a surface of the coil.